WO2004079020A1

WO2004079020A1 - Methods of switching and changing bottom-blown tuyere in converter

Info

Publication number: WO2004079020A1
Application number: PCT/JP2004/002482
Authority: WO
Inventors: Hisaki Kato; Makoto Kato; Minoru Tokuchi; Kenji Nishiyama; Shinichi Yamamoto
Original assignee: Jfe Engineering Corporation
Priority date: 2003-03-03
Filing date: 2004-03-01
Publication date: 2004-09-16
Also published as: CN1697886A; BRPI0403944A

Abstract

A method of switching a bottom-blown tuyere in a converter switching a bottom-blown tuyere by forming a new bottom-blown tuyere in a brick for drilling which is pre-installed in a refractory layer covering the bottom part of the converter at a position other than that where the bottom-blown tuyere is installed, comprising a step for pre-installing the brick for drilling in the refractory layer at the position different from that of a conventional tuyere so that, when either of the surface of an iron skin covering the outside of the converter or the surface of a flange installed on the iron skin is taken as a reference plane, the reference plane is positioned vertical to the drilled direction of the brick for drilling, a step for drilling the brick for drilling by a drilling machine from the outside of the iron skin in a direction vertical to the reference plane, and a step for inserting the new converter bottom-blown tuyere into a ground hole formed by drilling the hole through the brick for drilling.

Description

Description Switching method and replacement method of converter bottom blowing tuyere [Technical field]

The present invention relates to a method of switching a bottom blowing tuyere for switching a bottom blowing tuyere for stirring and refining a steel bath by injecting gas into a steel bath from the bottom of a converter, and a method for replacing a bottom blowing tuyere. The present invention relates to a method of replacing a tuyere of a furnace bottom.

[Background technology]

In a converter that purifies a steel bath by oxygen blowing from an upper blowing lance, it is necessary to increase the reaction interface area between the slag existing in the converter and the steel bath, or to increase the component segregation of the steel bath itself and the temperature distribution. In order to increase the efficiency of the refining reaction by reducing the variation of the steel bath, etc., it is widely practiced to blow the stirring gas into the steel bath from the bottom blowing tuyere provided at the bottom of the converter to vigorously stir the steel bath. Has been done. Also, from the bottom tuyeres provided in the converter bottom, not stirring gas only, has also been bubbling o ₂ gas for Sei鍊.

However, in a converter using a bottom blown tuyere, the refractory around the bottom blown tuyere is more likely to be eroded than the refractory in other parts, so the thickness of the brick other than the bottom blown tuyere is sufficient. Despite this, the operation of the furnace has to be stopped. Therefore, various proposals have been made in the past to extend the life of the bottom blowing tuyere.

For example, in Japanese Patent Application Laid-Open No. Hei 9-171680, drilling bricks to be used as tuyere receiving bricks are installed in advance at locations other than the bottom blown tuyere, and the tuyere during use is subject to wear. When it becomes too large to withstand use, the previously installed brick for perforation is perforated from the outside of the converter shell, and a new tuyere is inserted into a grinding hole formed through the perforated hole. Technology to continue operation is disclosed I have. In this case, the tuyere that can no longer be used is closed with an appropriate refractory material such as a cast refractory material, a sprayed refractory material or a sprayed refractory material. The tuyere receiving brick is a brick installed around the tuyere to support and protect the tuyere.

Japanese Patent Application Laid-Open No. 59-41414 discloses that a worn tuyere is withdrawn, a refractory is filled in the removed gap by a flame spraying method, and the tuyere is inserted into the filling portion again. A technique has been disclosed in which a hole is pierced, a new tuyere is inserted into the formed pierced portion, and the tuyere is replaced.

However, as described in JP-A-9-171672 and JP-A-59-41414, a pre-installed brick for perforation and a tuyere receiving brick are drilled from the outside of a converter. When drilling by drilling, make sure that the drilling direction of the brick to be drilled (usually the longitudinal axis direction) matches the drilling direction of the drilling machine in order to drill from the outside of the converter. Therefore, the drilling hole by the drilling machine does not stay in the brick to be drilled, but also drills to the surrounding brick to damage the surrounding brick. Also, the grinding hole becomes larger than necessary. Such troubles occur. In this case, the replacement tuyere will be worn out, and the service period of the bottom blown tuyere will be significantly shortened compared to the expected period. In addition, when setting a drilling machine, it takes time to determine the drilling direction, and there is a problem that the drilling time becomes longer than necessary.

[Disclosure of the Invention]

An object of the present invention is to provide a new bottom blow blade in a cutting hole formed by drilling a perforating brick previously installed in a portion other than the bottom blow tuyere at the bottom of the converter from the outside of the converter with a punch. When the bottom blow tuyere is switched by inserting a b, it is possible to form a grinding hole by piercing a central portion of the piercing brick along a predetermined piercing direction in a short time. A method for switching the tuyere of the converter bottom To provide. ^One

Another object of the present invention is to replace the bottom tuyere of the converter bottom with a method of piercing the center of a tuyere receiving brick of a conventional tuyere along a predetermined piercing direction in a short time. It is an object of the present invention to provide a method for replacing a tuyere of a converter bottom blow, which enables a grinding hole to be formed by the method.

According to the first aspect of the present invention, a new bottom-blowing tuyere is formed in a perforated brick previously installed in a portion other than the portion where the bottom-blowing tuyere is installed in the refractory layer covering the bottom of the converter. This is a method of switching the bottom tuyere of the converter by switching the bottom tuyere.Either the steel surface that covers the outside of the converter or the flange surface attached to this steel shell is used as the reference surface. A step of previously installing a perforated brick in a position different from a conventional tuyere in the refractory layer so that a surface and a perforated direction of the perforated brick are perpendicular to each other; Drilling from the outside of the skin in a direction perpendicular to the reference plane by a drilling machine, and inserting a new converter bottom blowing tuyere into a grinding hole formed through the drilling hole of the brick for drilling. And a method for switching the converter bottom blowing tuyere. '' According to the second aspect of the present invention, the tuyere comprising the refractory and the gas injection pipe provided in the refractory layer covering the bottom of the converter is eroded and the remaining thickness thereof becomes a predetermined value. A method of replacing the tuyere bottom blow tuyere that replaces the tuyere when it reaches, using either the steel surface covering the outside of the converter or the flange surface attached to this steel shell as the reference surface. The step of installing the tuyere receiving brick so that the reference surface and the tuyere receiving brick on which the tuyere is installed are perpendicular to each other, and the tuyere where the previous tuyere is installed. A step of piercing a mouth receiving brick from the outside of the steel shell by a piercing machine in a direction perpendicular to the reference plane; and a new converter bottom blowing into a grinding hole formed through the piercing hole of the tuyere receiving brick. A method of replacing a tuyere of a converter bottom blow, comprising a step of inserting a tuyere. According to the present invention, the tuyere receiving brick and the tuyere receiving brick The drilling direction of the perforated brick is perpendicular to this reference surface, using either the iron shell surface of the converter or the flange surface attached to the steel shell as the reference surface. And drill the hole perpendicular to this reference plane. Also, when replacing the tuyere tuyere at the bottom of the converter, the tuyere receiving brick to be perforated is used as a reference surface, using either the steel surface of the converter or the flange surface attached to the steel shell as the reference surface. The tuyere receiving brick is installed so that the direction of perforation is perpendicular to it, and perforation is perpendicular to this reference plane. For this reason, in any case, a ground hole should be formed along the target drilling direction almost in the center of the brick for drilling and the tuyere receiving brick without damaging the surrounding bricks during drilling. Becomes possible. As a result, the life of the inserted tuyere is stabilized, and long-term gas injection becomes possible.

Further, the drilling machine only has to drill a hole perpendicularly to the reference plane, and can perform the drilling in a short time without positioning the brick for drilling and the tuyere receiving brick to be drilled. The brick for drilling and the tuyere receiving hole to be drilled are installed in the drilling direction of the drilling machine and the converter iron of the brick for drilling and the tuyere receiving brick so that the grinding hole is installed in the center. It is installed in advance so that the center of the skin-side end surface substantially matches.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a part of a converter having a bottom blowing tuyere,

FIGS. 2A to 2D are cross-sectional views for explaining steps of a method of switching the bottom blowing tuyere according to the first embodiment of the present invention.

3A to 3D are cross-sectional views for explaining steps of a method for replacing a tuyere according to the second embodiment of the present invention.

[Best Mode for Carrying Out the Invention] An embodiment of the present invention will be described below with reference to the accompanying drawings.

First, the structure of a converter having a bottom blow tuyere will be described. Figure 1 shows bottom blowing It is sectional drawing which shows a part of converter with tuyere.

As shown in Fig. 1, the converter has a steel shell 9 forming an outer shell, a permanent brick 14 lined inside the steel shell 9 in contact with the steel shell 9, and an inner side of the permanent brick 14 And a work brick 13 as a consumable member. In the figure, the work bricks 13 are covered with one layer, but may be two layers or more. At the bottom of the converter, a plurality of bottom blow tuyeres 1 are provided through the work bricks 13 and the permanent bricks 14, and a steel bath in the converter is provided through the plurality of bottom blow tuyeres 1. r gas, N ₂ gas, agitation gas such as carbon dioxide, furthermore, 〇 ₂ gas rectification鍊用is blown rare, and summer to stir or Sei鍊steel bath.

The bottom blowing tuyere 1 covers a metal wind box 4 provided at the bottom, a plurality of gas blowing pipes 2 extending upward from the wind box and having an inner diameter of 5 mm or less, and a gas blowing pipe 2. And a gas introduction pipe 5 inserted into the bottom of the wind box 4 for supplying the above-described stirring gas or purification gas. The stirring gas or the purifying gas introduced into the wind box 4 through the gas inlet pipe 5 is equalized in the wind box 4 and then is introduced into the steel bath through the plurality of gas injection pipes 2. It is blown evenly. The plurality of gas injection pipes 2 and the refractory 3 are integrally formed. It should be noted that the bottom tuyere is not limited to such a structure, and may be appropriately selected according to the purpose. For example, there is no problem even if it is equipped with one gas introduction pipe and a coated refractory that covers it.

The bottom blow tuyere 1 is fitted into a part of the brick of the work brick 13, and the brick functions as the tuyere receiving brick 13 a.

Outside the tuyere receiving brick 13 a in which the bottom blow tuyere 1 exists, a flange 10 continuous with the steel shell 9 is provided. The plurality of flanges 10 are arranged at appropriate positions on the steel shell as communication paths with the gas injection device. Hula The flange lid 11 is port-fastened to the flange 10. A base brick 8 is interposed between the permanent brick 14 and the flange lid 11.

By the way, the brick 13 provided around the bottom blowing tuyere 1 was severely eroded by the steel bath that was strongly stirred by the blown gas, and had a higher erosion rate than the other parts and remained The thickness decreases rapidly. As a result, the tip of the bottom blowing tuyere 1 is also melted down, the remaining thickness of the bottom blowing tuyere 1 reaches a predetermined value, and it is necessary to switch or replace the bottom blowing tuyere.

Hereinafter, a method of switching and replacing a bottom blow tuyere according to an embodiment of the present invention will be described.

First, a brick is drilled in advance at a location different from the conventional bottom-blowing tuyere, and a new bottom-blowing tuyere is installed in the grinding hole of the brick for drilling to switch the bottom-blowing tuyere. An embodiment will be described with reference to FIGS. 2A to 2D. 2A to 2D are cross-sectional views for explaining steps of a method for switching a bottom blow tuyere according to the first embodiment of the present invention.

In the tuyere forming portion for switching, a brick 6 made of an integrally molded refractory is previously arranged when the work brick 13 and the permanent brick 14 are installed in the converter. In this case, in order to facilitate connection with the gas injection device outside the converter, the perforated brick 6 usually has a flange 10 serving as a communication path with the gas injection device on the steel shell 9. It is placed at the place where it was attached.

In this embodiment, first, as shown in FIG. 2A, the inner surface 9 a or the outer surface 9 b (iron surface) of the iron shell 9 is set as a reference surface, and the perforating brick 6 whose longitudinal direction is the direction of perforation is used. It is arranged in advance so that its longitudinal direction, that is, the direction of perforation is perpendicular to the reference plane (first step). In the present embodiment, since the flange 10 is disposed so that the flange surface 10a is parallel to the steel surface, the longitudinal direction of the drilling brick 6 is also perpendicular to the flange surface 10a. The same applies when the flange surface 10a is set as the reference surface. Iron skin 9 a, 9 b If the flange surface 10a is not parallel to the flange surface 10a, either the steel surface 9a, 9b or the flange surface 10a may be used as the reference surface.

Usually, the work bricks 13 of the converter are arranged in a direction in which the longitudinal direction is perpendicular to the steel shell 9 as shown in these figures, and the work bricks 13 are placed between the work bricks 13. The perforated brick 6 is also installed so that its longitudinal direction is perpendicular to the steel shell 9, but the work brick and the perforated brick are not installed perpendicular to the steel shell 9. It is necessary to previously install the flange 10 in a direction in which the flange surface is perpendicular to the work brick and the perforation brick. In this case, of course, the flange surface and the steel surface are not parallel.

The concrete construction method of the perforated brick 6 is as follows. First, the flange 10 and the flange lid 11 are fixed to each other with a port (not shown), and the upper and lower surfaces thereof are smooth and parallel planes. A certain base brick 8 is set on the flange lid 11. In the figure, two base bricks 8 are installed, but this is determined by the relationship with the installation thickness of the permanent bricks 14, and the tip of the perforating brick 6 is placed inside the receiving brick 15 If so, the number of installations may be any. Further, a hole 11 a having a size large enough to pass through the bottom blowing tuyere 1 is provided in the center of the flange lid 11.

Next, the perforating bricks 6 are arranged on the base bricks 8 so that their longitudinal axes are perpendicular to the base bricks 8. In this case, the receiving bricks 15 are arranged so as to surround the perforated bricks 6 at the positions where the perforated bricks 6 are arranged. The thickness of the receiving brick 15 is the same as that of the permanent brick 14, and the receiving brick 15 may be a combined brick or an integral brick. Since the perforated brick 6 is surrounded by the receiving brick 15, the perforated brick 6 does not easily come out of the furnace even if the perforated brick 6 is melted and shortened. Then, work bricks 1 around the perforation brick 6 Arrange 3 to configure the converter lining.

In the state where the drilling direction of the drilling brick 6 is set in advance in such a manner as to be perpendicular to the reference plane in this way, as shown in FIG. Perforate in the direction perpendicular to the reference plane (second step). This process is performed when the used tuyere is worn out and it is necessary to switch the tuyere.

In this process, first, the molten steel and slag in the converter are discharged, and the converter is tilted at an appropriate angle (usually tilted so that the drilling direction is horizontal), and the flange 1 0 or the flange lid 11 is connected to a mounting flange (not shown) of a drilling machine (not shown) having a drill 16 attached to the tip. This automatically aligns the drill 16 of the drilling machine with the center of the flange lid 11. Drilling accuracy is improved by connecting a drilling machine to the flange 10 or the flange lid 11; however, if the drilling machine cannot be connected, the drilling machine may be left on the converter work floor.

Then, drilling is performed while rotating the drill 16 in the direction perpendicular to the flange surface, that is, the flange lid 11, and toward the center of the flange lid 11, thereby forming a grinding hole 7. In this case, a plurality of drills 16 having different outer diameters are prepared, and the drills are sequentially drilled from the smaller diameter drill 16. In addition, in order to make the drilling work easy and reliable, a guide hole having a small diameter may be formed in advance at the drilling location of the base brick 8 and the brick for drilling 6. May be used. The guide hole of the perforated brick 6 is not penetrated, but only halfway.

At the end of the predetermined drilling process, the state of the drilled hole is checked, and if the drilled hole has penetrated and the grinding hole 7 has been formed as shown in FIG. Remove from lid 1 1 and as shown in Figure 2D Then, a new bottom blowing tuyere 1a in which the gas injection pipe 2 and the coated refractory 3 covering the outer circumference of the pipe are integrally formed is inserted into the grinding hole 7 (third step).

After inserting the new bottom blowing tuyere 1a, as shown in Fig. 1, the gas inlet pipe 5 of the bottom blowing tuyere 1 is passed through the hole provided at the center, and the convex part is flanged. The tuyere holding lid 12 for entering the hole 11a of the lid 11 to hold the bottom blown tuyere 1a and the flange lid 11 are fixed to each other with a port (not shown). Further, the gap between the bottom blowing tuyere 1a and the perforating brick 6 is filled with mortar previously applied to the outer surface of the bottom blowing tuyere 1a. Further, it is preferable that a repair material be poured into the gap between the bottom-blowing tuyere 1a and the perforating brick 6 from the inside of the converter so that this gap is minimized.

By switching the bottom tuyere in this manner, the work brick 13 around the perforation brick 6 is not damaged or the grinding hole 7 becomes unnecessarily large. It is possible to switch the bottom blow tuyere by drilling a grinding hole 7 in a short time along a predetermined drilling direction at the center of the bottom hole. As a result, not only is the improvement in converter productivity achieved, but also the wear rate of the new bottom blow tuyere becomes equal to the wear rate of the bottom blow tuyere used since the start of the converter. Even when switching, it is possible to operate the bottom blowing tuyere 1a until the end of the furnace life. As a result, the refining reaction of the converter is made more efficient until the end of the furnace body life, and an improvement in iron yield and a reduction in iron alloy unit can be achieved.

Next, when the conventional tuyere was melted and could no longer be used, the tuyere receiving brick on which the conventional tuyere was installed was pierced, and a new bottom blown tuyere was inserted into the formed grinding hole. A second embodiment in which a mouth is installed and the bottom blow tuyere is replaced will be described with reference to FIGS. 3A to 3D. 3A to 3D are cross-sectional views for explaining steps of a method of replacing a bottom-blowing tuyere according to the second embodiment of the present invention. In the present embodiment, the above-mentioned stirring gas or purifying gas is blown through the bottom blowing tuyere 1 to stir or purify the steel bath in the converter, whereby the bottom blowing tuyere 1 is melted. If the remaining thickness of the bottom-blowing tuyere 1 reaches the specified value, replace the bottom-blowing tuyere 1.

First, as shown in FIG. 3A, the inner surface 9a or the outer surface 9b (steel surface) of the steel shell 9 is set as a reference surface, and the tuyere receiving brick 13a having the longitudinal direction as a perforating direction is previously prepared. It is arranged so that its longitudinal direction, that is, the drilling direction is perpendicular to the reference plane (first step). As in the first embodiment, also in the present embodiment, since the flange 10 is arranged so that the flange surface 10a is parallel to the steel skin surface, the longitudinal direction of the Is also perpendicular to the flange surface 10a. When the steel surfaces 9a and 9b and the flange surface 10a are not parallel, the flange surface 10a may be used as the reference surface as in the first embodiment.

With the tuyere receiving brick 13a thus set in advance so that the perforation direction is perpendicular to the reference plane, then, as shown in FIG. Punching from the outside of the skin in a direction perpendicular to the reference plane by a punch (second step). This step is performed when the bottom spraying tuyere 1 in use is melted and the remaining thickness of the bottom blowing tuyere 1 reaches a predetermined value.

At this time, first, the molten steel and slag in the converter are discharged, and the converter is tilted and maintained at an appropriate angle (usually tilted so that the drilling direction is horizontal). Remove 1 2 from the flange lid 1 1. Then, remove the metal wind box 4 of the bottom blowing tuyere 1 so as not to hinder the perforation. Next, similarly to the first embodiment, a flange 10 or a flange lid 11 and a mounting flange (not shown) of a drilling machine (not shown) having a drill (not shown) attached to a tip thereof. And concatenate. As a result, the drill of the drilling machine is automatically aligned with the center of the flange lid 11. Then, while rotating the drill toward the flange surface, that is, the direction perpendicular to the flange lid 11 and toward the center of the flange lid 11, the center position of the conventional bottom blowing tuyere 1 is changed to the newly formed grinding hole. The bottom blow tuyere 1 and the tuyere receiving brick 13a are perforated so as to substantially coincide with the center position.

In this case, the conventional bottom-blowing tuyere 1 is pierced while it is still installed, and the newly formed grinding hole in the tuyere receiving brick 13a has its inner diameter set to the outer diameter of the previous bottom-blowing tuyere 1. Slightly larger than This is because the inner surface of the tuyere receiving brick 13a, which was in contact with the conventional bottom blow tuyere 1, may have reduced refractory properties, such as cracks or peeling during conventional or drilling. This causes damage to the state of fitting with the bottom blowing tuyere 1 to be used next time, which may lead to a decrease in the number of times of use, etc., to prevent this from happening. Therefore, the outer diameter of the tuyere used next time is slightly larger than that of the former tuyere.

When the predetermined drilling process is completed, the state of the drilled hole is checked, and as shown in FIG. 3C, if the drilled hole penetrates and the grinding hole 7 is formed, the drilling machine is connected to the flange 10 or the flange 10. Remove from the lid 11 and insert a new bottom-blowing tuyere 1b into the grinding hole 7, as shown in Fig.3D, in which a gas injection pipe and a coated refractory covering the outer circumference of this pipe are integrally formed (No. 3 steps).

After inserting the new bottom blow tuyere 1 b, attach the tuyere holding lid to the flange lid 11 to prevent the bottom blow tuyere 1 b from falling off. The gap between the tuyere tuyere 1b and the tuyere receiving brick 13a is filled with mortar previously applied to the outer surface of the tuyere tuyere 1b. In addition, a repair material is poured from the inside of the converter into the gap between the bottom blow tuyere 1b and the tuyere receiving brick 13a, so that this gap is made as small as possible.

By replacing the tuyere in this way, the work brick 13 around the tuyere receiving brick is not damaged, and the grinding hole 7 becomes unnecessarily large. It is possible to replace the bottom blown tuyere by drilling the grinding hole 7 in a short time along the predetermined drilling direction in the center of the tuyere receiving brick 13a without causing any trouble. Become. As a result, not only is the productivity of the converter improved, but also the wear rate of the replaced bottom blow tuyere 1b is equal to the wear rate of the bottom blow tuyere used from the start of operation of the converter. It is possible to operate the bottom-blowing tuyere 1b until the end of the life of the furnace body even when replacing the furnace, and to improve the iron yield by improving the efficiency of the converter scouring reaction until the end of the life of the furnace body. Reduction is achieved.

The present invention is not limited to the above description, and various changes can be made. For example, the base brick 8 is installed, but the base brick 8 is not installed, and the perforated brick 6 serving as the tuyere receiving brick may be arranged so as to be in contact with the flange lid 11. Work bricks 13 may be placed.

[Industrial applicability]

ADVANTAGE OF THE INVENTION According to this invention, the brick for perforation and the tuyere can be prevented without damaging the work brick in the peripheral part of the brick for perforation and the tuyere receiving brick, and generating the grinding hole larger than necessary. In the center of the receiving brick, a grinding hole can be pierced in a short time along a predetermined piercing direction, and the tuyere can be switched and exchanged. As a result, it has high industrial utility, such as improved converter productivity and improved iron yield.

Claims

The scope of the claims

1. A new bottom-blow tuyere is formed in a brick for drilling that has been previously installed in a portion of the refractory layer covering the bottom of the converter other than the bottom-blow tuyere, and the bottom-blow tuyere is switched. A method of switching the bottom tuyere,

Either the steel surface covering the outside of the converter or the flange surface attached to the steel surface is used as a reference surface, and the refractory layer is set so that the reference surface and the drilling direction of the drilling brick are perpendicular to each other. Pre-installing a perforated brick at a location different from the previous tuyere in the

Perforating the perforated brick in a direction perpendicular to the reference plane by a perforator from outside the steel shell;

A step of inserting a new converter bottom blow blade into a grinding hole formed through the perforation hole of the perforated brick.

2. In the method for switching a converter bottom blowing tuyere of claim 1, the tuyere is formed by integrally forming a plurality of gas blowing tubes and a refractory material covering these gas blowing tubes. The method of switching the converter bottom blowing tuyere.

3. When the tuyere consisting of the refractory provided in the refractory layer covering the bottom of the converter and the gas injection tube melts and the remaining thickness of the tuyere reaches a predetermined value, the tuyere is replaced. It is a method of replacing the furnace bottom tuyere,

Either the steel surface that covers the outside of the converter or the flange surface attached to this steel surface is used as the reference surface, and the reference surface is perpendicular to the perforation direction of the tuyere receiving brick where the tuyere is installed. As described above, the procedure for installing the tuyere receiving brick is as follows.

A step of perforating a tuyere receiving brick on which a conventional tuyere is installed in a direction perpendicular to the reference plane by a punch from the outside of the steel skin;

A new converter is added to the grinding hole formed by penetrating the tuyere receiving brick. A step of inserting a bottom blown tuyere.

4. The method for replacing a converter bottom tuyere according to claim 3, wherein the tuyere is formed by integrally forming a plurality of gas injection tubes and a refractory material covering these gas injection tubes. How to replace the converter bottom blowing tuyere.